Citrix ADC Gateway EPA scans deny access randomly with error code 12029.

The 12029 error code means that the EPA plugin could not connect to VPN virtual server.

This is a network related issue and this kind of issues are mostly caused by firewall or other security related software. To verify, disable firewall and anti-virus, and then try connecting again. If this solves the issue, then add a rule for white listing nsepa.exe (EPA plugin process) and nsload.exe (VPN plugin process)